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Shape Purpose - It controlled by a fixed Lookup table and is currently limited to:
Multibeam Acquistion Acquisition Extents (often smaller than the overall Survey Acquisition Extent)
Multibeam Line Paths (often a subset of the Survey Track Lines)
Survey/Cruise/Voyage Acquisition Extent
Survey/Cruise/Voyage Acquisition Tack Lines
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You can zoom in and out of the map frame to your area of interest and Capture the Bounding Box coordinates directly from the Map. Alternatively, you can enter them manually via the following fields.
Future releases will investigate the automatic generation of the bounding box coordinates from an uploaded shapefleshapefile.
North Latitude - The northern most Latitude (positive for northern hemisphere and negative values for the southern hemisphere)
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West Longitude - The West most Longitude (positive for locations west of the prime meridian (Greenwich) and negative values for the locations east of the prime meridian (Greenwich) )
East Longitude - The Eastern mode Longitude
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Reminder that the small red triangle 
in the top left corner of the field indicates the item is Mandatory to complete a submission (validation of these mandatory rules only occurs when the user is ready to Submit the metadata).
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